1. Field of the Invention
The present disclosure is directed to semiconductor devices and methods for fabricating the same, and more particularly, to semiconductor devices including an SRAM cell and methods for fabricating the same.
2. Description of the Related Art
Semiconductor devices are light weight, support miniaturization and multiple functions, and are inexpensive, and are widely used in the variety of industries such as electronics appliances, automobiles and vessels. Semiconductor devices may include memory cells. Examples of semiconductor devices having memory cells include semiconductor memory devices, logic devices and driver devices. For example, logic devices may include logic circuits for logical operation and memory cells for storing data required for the logical operation. Similarly, driver devices may include driver circuits and memory cells.
Memory cells may be classified as either nonvolatile memory devices or volatile memory devices. Nonvolatile memory devices can retain data when power is interrupted. Typical examples of a nonvolatile memory cell include a flash memory cell, a phase changeable memory cell, and a magnetic memory cell. Volatile memory devices do not store data when the power is interrupted. Typical examples of a volatile memory cell include a DRAM (Dynamic Random Access Memory) cell and an SRAM (Static Random. Access Memory) cell. An SRAM cell performs higher speed operations relative to the DRAM cell and does not need a refresh operation. Due to the above characteristics of an SRAM cell, some memory devices may include an SRAM cell as a memory cell. However, an SRAM cell may occupy a greater area than a DRAM. Therefore, research has been directed to improving the integration density of SRAMs.